This invention relates to an optical disk in which signals are recorded both onto recording tracks in depressed portions formed by guide grooves and onto recording tracks on projecting portions between the guide grooves, and to an optical disk apparatus, and an optical disk tracking method.
As a data recording method for a large-capacity rewritable optical disk, a land/groove recording method in which data is recorded both in guide grooves (sometimes denoted by G) and on lands (sometimes denoted by L) to increase a recording density, has been proposed. When this method is used, the recording density can be increased because the recording track pitch can be halved compared to an optical disk having the same groove pitch but for which this method is not used. Grooves and lands may also be referred to as depressed portions and projecting portions, respectively.
As a conventional land/groove recording optical disk, there is provided an optical disk shown in FIG. 13, for example. It is described in Japanese Examined Patent Publication 63-57859. As shown in FIG. 13, grooves 94 and lands 95 are formed by means of guide grooves inscribed on the substrate of the disk, and a recording film 91 is formed thereon. Recording marks 92 are formed on the recording film 91 extending both on the grooves 94 and the lands 95. The grooves 94 and the lands 95 form continuous data recording tracks, respectively. A light-focused spot 93 of an optical disk drive apparatus for performing data recording and reproduction onto this recording medium records or reproduces data while scanning either of the recording tracks. With a conventional land/groove recording format, guide grooves are continuous on a disk. Thus, each of the data recording tracks of the grooves 94 and the data recording tracks of the lands 95 form a single continuous recording spiral.
A single spiral land/groove format is described next.
FIG. 14 shows the configuration of an optical disk having a format in which each data recording track of grooves (hereinafter also referred to as a groove track) 94 having a length corresponding to a revolution of the disk and each data recording track of lands (hereinafter also referred to as a land track) 95 also having a length corresponding to a revolution of the disk are connected alternately to form a data recording spiral. An example of optical disks having the format shown in FIG. 14 in which groove tracks 94 and land tracks 95 are connected alternately to form a data recording spiral, is described in Japanese Unexamined Patent Publication 4-38633 and Japanese Unexamined Patent Publication 6-274896. The format of such optical disks is herein referred to as the single spiral land/groove format or the SS-L/G format.
An SS-L/G format optical disk has continuous data recording tracks on the disk, so that it is suitable for continuous data recording and reproduction. When an optical disk is used as a video file, for example, continuous data recording and reproduction is essential. However, in a conventional land/groove recording optical disk shown in FIG. 13, the land tracks 95 and the groove tracks 94 form separate data recording spirals. Thus, when data recording or reproduction is performed continuously from the land tracks 95 to the groove tracks 94, for example, it is interrupted at least at one portion of the disk due to an access between the land tracks 95 and the groove tracks 94. The same interruption occurs when data recording or reproduction is performed continuously from the groove tracks 94 to the land tracks 95. In order to avoid such an interruption in the data recording or reproduction, it is necessary to provide an additional buffer memory, which raises the cost. If optical disk is of a single spiral land/groove format, no such additional buffer memory is necessary.
In an SS-L/G format optical disk, however, a tracking servo polarity must be switched at every revolution of the disk. Since the detection of this tracking servo polarity switching point is difficult, application of the tracking servo is also difficult. For this reason, the SS-L/G format optical disk has found few practical applications. Although formatting an SS-L/G format optical disk is disclosed in Japanese Unexamined Patent Publication 4-38633 and Japanese Unexamined Patent Publication 6-274896 mentioned above, nothing is disclosed about a specific method of detecting a tracking servo polarity switching point.
In order to apply a tracking servo to an SS-L/G format optical disk, it is necessary to accurately detect between alternating points connecting groove tracks and land tracks, and to switch a tracking servo polarity to be set for tracking a groove track or a land track. Examples of methods of detecting connecting alternating points connecting groove tracks and land tracks are disclosed in Japanese Unexamined Patent Publication 6-290465 and Japanese Unexamined Patent Publication 7-57302.
In the method disclosed in Japanese Unexamined Patent Publication 6-290465, depressed portions and projecting portions of a constant frequency are provided at the connecting points between land tracks and groove tracks. FIG. 15 shows the configuration of an optical disk recording medium described in the above-mentioned publication. Referring to FIG. 15, the connecting points are at A1, A2, A3, B1, B2, etc. Between the connecting points next to each other either a land or a groove continues, and positional data such as a track address is represented by wobbling grooves.
In the method disclosed in Japanese Unexamined Patent Publication 7-57302, a flat part having no grooves or a predetermined pattern of pits are provided at the connecting points between groove tracks and land tracks. FIG. 16A and FIG. 16B show the configuration of an optical disk recording medium described in the above-mentioned publication. FIG. 16A shows an example of a flat part provided at a connecting point, while FIG. 16B shows an example of a predetermined pattern of pits. In this prior art example, nothing is disclosed about positional data such as a track address, and it can be regarded that either a groove or a land continues between the connecting points on a spiral.
Now, description is directed to a case where pit pattern data for detecting a connecting point is provided on an optical disk in which each of the data recording tracks is composed of a plurality of data recording sectors having their own identification data. In the method of providing identification data by wobbling grooves, no interrupting portion is present in the groove of a data recording part in one revolution except for a connecting point. Thus, the problem of erroneous detection of a connecting point will not arise. However, the function of recording data onto a sector is restricted. For instance, data recording or reproduction in units of short sectors is difficult.
In contrast with an optical disk of the above-mentioned configuration, in the case of an optical disk such as a conventional ISO magneto-optical disk having a format in which preformatted identification data parts representing addresses and data recording parts recording user data are arranged separately on data recording tracks, if identification data and a connecting point between a groove and a land are represented in the same recording form, the problem of erroneous detection of the connecting point will arise. In order to avoid such a problem, it is necessary to ensure discrimination between the pit pattern of identification data and the pit pattern for detecting a connecting point between a groove and a land. In the example disclosed in Japanese Unexamined Patent Publication 7-57302, since the pit sequence as shown in FIG. 16B is provided only at connecting points, the problem of erroneous detection of the connecting point will not occur. However, when identification data is preformatted with a pit pattern similar to that for detecting a connecting point and arranged in a data recording track, it is necessary to reproduce the pit data in the connecting point with precise pit synchronization so as to detect the connecting point with a high reliability. This applies to all cases where a connecting point is detected according to the pit pattern, regardless of how the connecting point is represented, such as by means of a pit pattern of a constant frequency or a predetermined pit pattern.
In order to reproduce pit data with precise pit synchronization, establishment of stable tracking is a prerequisite. This means that a connecting point between a groove and a land should be correctly detected and tracking should be switched accordingly. In order to do this, it is necessary to distinguish between the pit pattern for detecting the connecting point and the pit pattern for the identification data and to reproduce the pit data for the connecting point with the precise pit synchronization. This falls into a circular dependency. It indicates that, according to the prior art, in an optical disk having a format in which each of the data recording tracks is composed of a plurality of track sectors having a preformatted identification part and a data recording part arranged separately, reliable detection of a connecting point between a groove and a land which is essential for implementing a single spiral land/groove format is difficult.
Now, a method of inserting identification signal prepits which has been proposed for a conventional land/groove recording optical disk is described. In the conventional land/groove recording method, three methods of inserting identification signal prepits as shown in FIG. 17A to FIG. 17C are known. In the method illustrated in FIG. 17A, also referred to as a land/groove individual addressing method, each of land track sectors and groove track sectors has their own sector address. If the width of prepits representing an identification signal were set to be identical to the width of a groove, identification signal prepits of the adjacent track sectors would be connected, and no identification signal could be detected. For this reason, the width of identification signal prepits is set to be smaller than that of a groove, and normally is set to be about half the width of a groove.
However, unless the diameter of a laser beam for inserting prepits is made different from that for forming a groove during the fabrication of a master disk in the mastering process, continuous formation of a groove and prepits having different widths as described above cannot easily be performed. For this reason, two separate laser beams for forming grooves and forming the prepits must be used for cutting the master disk. If two laser beams are not aligned during the formation of grooves and prepits, there will be a tracking offset between the reproduction of identification signal prepits and the recording or reproduction of data recording signals. The quality of reproduced data will therefore deteriorate. More specifically, due to the deviation of tracking, an error rate of the reproduced data will increase, lowering the reliability of the reproduced data. Thus, highly accurate positioning of the two laser beams is required, which will be a factor for raising the cost of fabrication of a master disk.
In view of the above-mentioned problem, and in terms of the accuracy and the cost of the fabrication of an optical disk, the method illustrated in FIG. 17B or FIG. 17C, capable of forming grooves and prepits with a single laser beam is preferable. FIG. 17B and FIG. 17C respectively show the methods capable of inserting prepits having substantially the same width as that of a groove.
FIG. 17B shows a conventional optical disk described in Japanese Unexamined Patent Publication 6-176404 and which uses a method also referred to as a land/groove common address method. In this method, identification signal prepits PP are disposed around the center of a pair of adjacent groove and land tracks, and the same identification signal prepits are shared by a groove track G and a land track L adjacent to each other.
FIG. 17C shows a conventional optical disk described in Japanese Unexamined Patent Publication 7-110944 and which uses a method referred to as a time-division L/G individual address method. In this method, individual addresses are provided for land tracks L and groove tracks G. The positions at which the identification signal prepits PP for the adjacent land tracks and groove tracks are arranged are shifted relative to each other in a direction parallel to the tracks such that the identification signal prepits do not neighbor each other.
When considering a method of providing identification signal data and data for detecting a connecting point, immunity to defects should also be considered. For switching a tracking polarity by reading the identification signal data and the data for detecting a connecting point, discrimination between a groove and a land should not fail in the presence of a slight defect on the disk. It is essential to perform correct detection of a connecting point, even if there are typical defects on the medium such as fine flaws, and defective holes formed on a recording film and causing reduction of an index of reflection.
When considering a method of providing the identification signal data and the data for detecting a connecting point, consideration should be also given to a servo characteristic.
The SS-L/G format provides a higher track density because both lands and grooves are used for recording data. However, because of this higher track density, when a tracking offset is increased, the quality of a reproduced signal deteriorates because of crosstalk from an adjacent track and the error rate increases due to an increase in jitter, for example. Crosserase of data on an adjacent track, which means erasure of part of data on an adjacent track, may also occur during data recording. An error which will cause a tracking offset is generated due to combined effects of the optical head system, the arrangement of tracks in an optical disk, and the servo systems. For this reason, such an error generally has different levels for a land track and a groove track.
In order to avoid crosstalk and crosserase, different offset compensation is required for each of a land track and a groove track. In the conventional land/groove recording method, i.e., the method in which groove tracks and land tracks form separate data recording spirals, offset compensation can be made for the respective spirals of the land tracks or the groove tracks during the continuous tracking operation, taking a certain period. Then, after the adjustment, the amount of compensation can be retained. Thus, offset compensation can be achieved easily.
With the SS-L/C format optical disk, however, tracking polarity switching between a land track and a groove track must be made at every revolution of the disk. For this reason, it is necessary to make tracking offset compensation accurately and quickly. As described above, with the SS-L/G format optical disk, a method of inserting identification signals taking account of tracking offset compensation is required.
The above-mentioned conventional methods of inserting identification signals for a land/groove recording optical disk did not provide the characteristics required of a SS-L/G format disk, for dealing with the medium defects or tracking offset compensation.
In the case of the land/groove common address method as illustrated in FIG. 17B, for example, identification signal prepits are disposed on one side of a land track or a groove track. Thus, a tracking offset keeps increasing the reproduction of identification signals. On the other hand, in the case of the L/G individual address method as illustrated in FIG. 17C, detection of a tracking offset is difficult, which is also true for the case of FIG. 17B.
The operation associated with driving an optical disk is next described. When a control system for changing the rotational speed during the driving operation of the optical disk is used, quick and accurate detection of a connecting point between a land and a groove will become more difficult. However, with an optical disk used for a video application mainly requiring continuous data recording and reproduction, the above-mentioned control system should be used.
In case emphasis is placed on the compatibility with an read-only optical disk, a phase-change medium is suitable as a rewritable optical disk. This is because, with this phase-change medium, the optical system can be commonly used with the read-only optical disk. However, with the phase-change medium having data recording and reproduction performance which can be used in practice, the range of data recording linear velocities over which the data recording and reproduction characteristic associated with the PWM data recording operation is satisfied is narrow. More specifically, when an optical disk is controlled with the CAV (Constant Angular Velocity), the rotational speed of the disk in the inner radial part and the rotational speed of the disk in the outer radial part will be identical, and the recording linear velocity of the disk in the outer radial part will be approximately 2.5 to 3 times faster than that in the inner radial part. The currently-available phase-change medium cannot be used over this wide range of data recording linear velocities.
Where the rotation of the disk is CAV-controlled, if the rotational speed of the disk in the inner radial part is set to achieve a required data rate, when the outer radial part of the disk is scanned, the signal processing circuit must perform high speed processing nearly three times faster than that for the inner radial part. For this reason, implementation of the required function with hardware of a low cost will be difficult. Further, when considering the video application of the disk, it is preferable that the optical disk have a constant data rate between the outer radial part and the inner radial part.
Thus, for a rewritable optical disk used for the data recording of a digital video, because of the two reasons of the characteristic of the medium and the circuit performance, a ZCLV (Zoned Constant Linear Velocity) method is practical. In this method, an optical disk is divided radially into a plurality of zones, and the rotational speed of the disk is switched from one zone to another to obtain a constant data transfer rate and a substantially constant linear velocity throughout the zone.
When the ZCLV method is used, the following problems will arise. In the ZCLV method, the rotational speed of the disk need be changed while the light spot crosses a zone boundary. In addition, when the light spot has moved from one zone to another, a certain time is required until the rotational speed of the disk settles (or stabilizes) at the stipulated rotational speed for the zone to which the light spot has moved. During the settling time, the interval between the sectors varies. Then, sector synchronization may be temporarily lost, in which case it is necessary to re-establish the sector synchronization quickly. It is also necessary to detect a connecting point between a land track and a groove track quickly and accurately.
An optical disk drive apparatus for driving a conventional land/groove recording optical disk is described next. FIG. 18 is a block diagram showing the configuration of the conventional optical disk drive apparatus described in Japanese Unexamined Patent Publication 6-176404. Referring to FIG. 18, reference numeral 100 indicates an optical disk, 101 indicates a semiconductor laser, and 102 indicates a collimator lens for converting a laser beam from the semiconductor laser 101 into a parallel beam. Reference numeral 103 indicates a half mirror, 104 indicates an objective lens for focusing the parallel beam which has passed through the half mirror 103 onto the optical disk, and reference numeral 105 indicates a photodetector for receiving the beam which has been reflected from the optical disk 100, and has passed through the objective lens 104 and the half mirror 103. The photodetector 105 includes two light-receiving parts divided by a boundary line extending in a direction parallel and to the track direction of the disk so as to obtain a tracking error signal. Reference numeral 106 indicates an actuator supporting the objective lens 104, and a portion 107 enclosed by a dotted line represents an optical head mounted on a head base. Reference numeral 108 indicates a differential amplifier for receiving detection signals from the photodetector 105, and reference numeral 109 indicates a polarity reversal circuit for receiving the tracking error signal from the differential amplifier 108, and a control signal T1 from a system controller 121 which will be hereinafter described, and for supplying the tracking error signal to a tracking controller 110. The polarity of the tracking control is such that when the tracking error signal is supplied from the differential amplifier 108 to the tracking controller 110 without having its polarity reversed, the light spot is pulled into a groove track. Reference numeral 110 indicates the tracking controller for receiving the output signal from the polarity reversal circuit 109 and a control signal T2 from the system controller, and for supplying tracking control signals to a driver 120 and a traverse controller 116. Reference numeral 111 indicates a summing amplifier for receiving the detection signals from the photodetector 105 and for supplying the sum signal, and reference numeral 112 indicates a waveform shaping circuit for receiving a high-frequency component of the output signal from the summing amplifier 111 and for supplying digital signals to a reproduced signal processor 113 and an address reproduction circuit 114 which will be hereinafter described. Reference numeral 113 indicates the reproduced signal processor for supplying reproduced data to an output terminal. Reference numeral 114 indicates the address reproduction circuit for receiving the digital signal from the waveform shaping circuit 112 and for supplying an address signal to an address calculator 115 which will be hereinafter described. Reference numeral 115 indicates the address calculator for receiving the address signal from the address reproduction circuit 114 and the control signal T1 from the system controller 121 and for supplying the correct address signal to the system controller 121. Reference numeral 116 indicates a traverse controller for providing a driving current to a traverse motor 117 which will be hereinafter described, in response to a control signal T3 from the system controller 121. Reference numeral 117 indicates the traverse motor for moving the optical head 107 in the radial direction of the optical disk 100. Reference numeral 118 indicates a recording signal processor for receiving recording data and supplying a recording signal to a laser diode (LD) driver 119 which will be hereinafter described. The LD driver 119 receives a control signal T4 from the system controller 121 and the recording signal from the recording signal processor 118 and supplies a driving current to the semiconductor Laser 101. Reference numeral 120 indicates a driver for supplying a driving current to the actuator 106. Reference numeral 121 indicates the system controller for supplying the control signals T1 through T4 to the tracking controller 110, the traverse controller 116, the address calculator 115, the polarity reversal circuit 109, the recording signal processor 118, and the LD driver 119.
The operation of the conventional optical disk drive apparatus having the above-mentioned configuration is described with reference to FIG. 18. The laser beam emitted from the semiconductor laser 101 is made to be parallel by the collimator lens 102, passed through the beam splitter 103, and focused onto the optical disk 100 by the objective lens 104. The laser beam reflected from the optical disk 100 contains data on recording tracks, and passed through the objective lens 104 and directed to the photodetector 105 by the beam splitter 103. The photodetector 105 converts the intensity and the distribution of light in the incoming light beam to electrical signals, and supplies them to the differential amplifier 108 and the summing amplifier 111. The differential amplifier 108 applies a current-to-voltage conversion (I-V conversion) to the input currents and supplies the potential difference between the two input signals, as a push-pull signal.
The polarity reversal circuit 109 determines whether a track being accessed is a land track or a groove track in accordance with the control signal T1 from the system controller, and reverses a polarity only when the track being accessed is a land track, for example. The tracking controller 110 supplies a tracking control signal to the driver 120 according to the level of the tracking error signal. The driver 120 supplies the driving current to the actuator 106 in accordance with the tracking control signal and controls the position of the objective lens 104 laterally of the data recording tracks. The light spot thereby scans the data recording tracks accurately.
On the other hand, the summing amplifier 111 applies a current-to-voltage conversion (I-V conversion) to output currents from the light-receiving parts 105, adds the input signals, and supplies the result as the sum signal to the waveform shaping circuit 112. The waveform shaping circuit 112 slices the data signal, and the address signal in analog form with a predetermined threshold value and supplies pulse trains to the reproduced signal processor 113 and the address reproduction circuit 114, respectively. The reproduced signal processor 113 demodulates the input digital data signal, applies error correction, and supplies it as reproduced data.
The address reproduction circuit 114 demodulates the input digital address signal and supplies the result of the demodulation as disk position data to the address calculator 115. The address calculator 115 calculates the address of a sector being accessed, based on the address signal read from the optical disk 100 and the land/groove signal from the system controller 121 indicating whether a track being accessed is a land track or a groove track. The manner of address calculation will be described later. Based on the address signal, the system controller 121 determines whether the light beam is scanning a desired sector.
At the time of moving the optical head, in response to the control signal T3 from the system controller 121, the traverse controller 116 supplies a driving current to the traverse motor 117 so as to move the optical head 107 to a target track. At this time, the tracking controller 110 temporarily stops a tracking servo in response to the control signal T2 from the system controller 121. During normal data reproduction, the traverse motor 117 is driven in response to the tracking error signal from the tracking controller 110 so as to move the optical head 107 gradually in the radial direction of the disk with the progress of data reproduction. The recording signal processor 118 adds error correction codes to the recording data which have been supplied at the time of data recording, and supplies an encoded recording signal to the LD driver 119. When the system controller 121 has set the mode of the LD driver 119 to the data recording mode by means of the control signal T4, the LD driver 119 modulates a driving current to be applied to the semiconductor laser 101 in accordance with the recording signal. The intensity of a light spot of the beam emitted onto the optical disk 100 is thereby changed according to the recording signal, and recording marks are formed.
On the other hand, during data reproduction, the mode of the LD driver 119 is set to the data reproduction mode by means of the control signal T4, and the LD driver 119 controls the driving current in such a manner that the semiconductor laser 101 emits a laser beam of a constant intensity. The recording marks and prepits on the data recording tracks can be thereby detected.
In such a conventional optical disk drive apparatus, an identification signal is reproduced based on the sum signal having been processed by the waveform shaping circuit 112. In an SS-L/G format disk as well, a connecting point between a land track and a groove track will be reproduced, based on the sum signal having been processed by the waveform shaping circuit 112. For this reason, in order to detect a connecting point with a high reliability, it is necessary to set a pit pattern for an identification signal representing address data and a pit pattern for detecting a connecting point to be quite different.
Even where reproduction of data or an address is not ready because it is immediately after a light spot has been pulled into a track, a connecting point must be detected. Thus, a pit pattern for detecting a connecting point should be reproducible even when the synchronization has not been achieved. For this purpose, it is necessary to allocate long pits, and to provide prepits of a pit pattern of a low frequency, i.e., of long pits. In a large-capacity optical disk which aims at the smallest possible redundancy and increase of an effective recording density, allotting long pits to the pit pattern is not desirable.
A conventional land/groove recording optical disk medium and a conventional optical disk drive apparatus are configured as described above. Thus, when the method of inserting identification signals used in the conventional optical disk is applied to a single spiral land/groove recording format, it is difficult to detect a connecting point between a land track and a groove track with a high reliability.
Further, if a pit pattern permitting discrimination from the identification signal and detection of a connecting point easily is allotted to the connecting point, long pits are necessary. An effective recording density is thereby reduced.
With a single spiral land/groove format, tracking offset compensation needs to be carried out quickly and accurately. However, detection of a tracking offset is difficult.